The aim of the project is to develop a series of compounds that may be useful for the treatment of AIDS. The proposed approach builds on the demonstrated ability of antisense oligonucleotides to inhibit HIV replication and the appeal that this approach has for rational drug design given the unsurpassed predictability of recognition and binding between nucleic acids. The ability of antisense oligonucleotides to inhibit the replication of human immunodeficiency virus can be enhanced considerably by chemical modifications that improve cellular uptake or survival. In molar terms, these compounds are about as active as AZT but because of their larger molecular weight may be impractical for therapeutic purpose due to the mass of material required for an effective dose. Oligonucleotides may dissociate from the target RNA or may be displaced by polymerases, spliceosomes or ribosomes. Thus, they have to be maintained in high concentration at the site of action. The approach to increasing activity further that is proposed here is to incorporate into an antisense oligonucleotide a catalytically active sequence of RNA that will cleave the target RNA after hybridization and so inactivate it irreversibly. Strategies are proposed for increasing the turnover number so that the enzymatic RNA (ribozyme) can cleave more than one equivalent of viral RNA. The cellular uptake and survival of these agents will be investigated and, if necessary, the modifications that proved useful previously will be employed here also. All compounds will be tested for their ability to inhibit the growth of HIV in cultures of H9 cells. The advances that could result from this work are: 1. A third generation of antisense oligonucleotides with clinically useful activity for the treatments of AIDS. 2. Improvements in the design of antisense oligonucleotides that should be applicable in other virus and non-virus diseases. 3. A new approach to rational drug design that builds upon the exquisite selectivity of base pairing in nucleic acids. 4. Further understanding of the action of catalytically active RNA (ribozymes). 5. Direct comparisons of antisense RNA with DNA and modifications of these to further expand experience with antisense agents for therapeutic and research purpose.